The present invention relates to an electric machine and, in particular, to a concentric dual-winding, multi-rotor electric machine.
Vehicles, such as aircraft, are provided with generator systems. Likewise, these vehicles also have on-board equipment that are mechanically driven by an electric motor. A generator system may include a main generator, an exciter, and a permanent magnet generator. The main generator includes a rotor that has a field winding that receives a direct current to create a magnetic field that spins synchronously with the rotor. The exciter has a stationary field winding with a rotating armature winding that produces alternating current. The alternating current from the rotating armature winding is rectified to a direct current using a rotating rectifier and is fed to the wound rotor of the main generator. The current in the field winding of the exciter is controlled by a generator control unit to provide the required output from the main generator. The generator control unit may be designed such that it can be powered by either the main generator or a permanent magnet generator in the event that the main generator is not yet providing electricity. The permanent magnet generator includes permanent magnet rotors with wound stators connected to the generator control unit. Current generator systems are considerably bulky and in an attempt to provide increased performance and functionality a more compact and power dense electric machine is desired.
An electric motor typically includes a single, stationary stator, and a single rotational component, rotor. The stator has electrical windings that receive an alternating current from a separate source of which creates a rotating magnetic field within the stator/rotor airgap and as a consequence the rotor naturally follows the rotating magnetic field with its own rotation amongst its center axis. This rotor rotation is then used to turn shafting and provide mechanical power to on on-board system (e.g. fan, compressor, pump, actuator, etc.). The angular speed of the rotating magnetic field is dependent on the excitation frequency of the alternating current and the pole count of the motor. Also, depending on the rotor type, the rotor will either follow the magnetic field created by the stator synchronous, (e.g. permanent magnet rotor, switched reluctance rotor), or asynchronous (e.g. induction squirrel cage rotor). Each motor rotor type has its own specific advantages/disadvantages and one may be better suited for a particular application over another. Compromises in size, weight, cost, efficiency, and complexity of stator excitation/start-up routines are often necessary to accommodate a particular motor rotor type for a given application. Current electric motors can be considerably bulky and in an attempt to provide increased performance and functionality a more compact and power dense electric machine is desired.